KR20160071890A - Optical polyester laminated film - Google Patents

Abstract

The present invention relates to an optical polyester laminated film. More specifically, the present invention relates to an optical polyester laminated film which exhibits excellent adhesiveness to an ultraviolet (UV) curable resin used in a postprocessing process such as prism sheets, microlens, or hard coating. Particularly, the optical polyester laminated film includes an application layer having excellent melting resistant adhesiveness, and is capable of reducing color stains formed by reflection of light after processing the UV curable resin.

Description

[0001] OPTICAL POLYESTER LAMINATED FILM [0002]

The present invention relates to an optical polyester laminated film, and more particularly to an optical polyester laminated film which is excellent in adhesion to a UV curable resin used in a post-process such as a prism sheet, a microlens, or a hard coating, And is capable of reducing color unevenness due to reflection of light after UV curable resin processing, and to a polyester laminated film for optical use.

In general, transparent plastic films such as polyester (PET, PEN, etc.), polycarbonate (PC), polymethyl methacrylate (PMMA), triacetyl cellulose (TAC) and amorphous polyolefin (amorphous PO) Is used as a substrate for a flat panel display such as a liquid crystal display or a plasma display display, a film for a touch panel, or a film for a window because it has a light weight and does not break easily. Among them, the biaxially stretched polyester film not only has excellent properties such as mechanical properties, electrical properties, dimensional stability, heat resistance, transparency and chemical resistance, but also has higher general versatility and cost advantage than other transparent plastic films It is very useful for many applications.

The optical polyester film can be used for various purposes such as a prism sheet, a microlens, and a hard coating by applying a variety of resins through a post-processing process as a base film and imparting various characteristics suited to its functions. As the resin used in the post-processing, a UV curable resin is generally used. Therefore, in order to uniformly adhere the UV curable resin layer applied through the post-processing to the optical polyester laminated film, a polyester resin, an acrylic resin, and a polyurethane resin are generally used on the surface of the polyester film, A method of forming a coating layer is most widely used industrially.

The UV curable resin used for forming the prism sheet, the microlens, and the hard coating layer may be applied on a polyester film coated with a primer coating layer and then cured by irradiating UV rays onto the polyester film. The UV-curable resin formed by this method is divided into a solvent type including a solvent and a solventless type that does not contain a solvent. Generally, the effect of the solventless type penetrating or swelling into the primer layer is lower than that of the solvent type, Is not necessarily sufficient.

On the other hand, the refractive index in the plane direction of the optical polyester film is generally about 1.63 to 1.68, and the refractive index of the UV curable resin layer generally has a value less than that. Due to this difference in refractive index, color unevenness occurs on the surface of the laminated film at the interface between the biaxially stretched polyester film and the UV curable resin layer. These color spots are detected as much as the laminated film is transparent, and are detected under three wavelength fluorescent lamps than sunlight or incandescent lamps. In order to reduce such color unevenness, it is important to design the optical element such that the refractive index of the primer layer is between the refractive index of the polyester film and the refractive index of the UV curable resin. Generally, since the primer layer has a refractive index of about 1.5, a primer layer having a high refractive index is required, and in this case, adhesion with the UV curable resin is often insufficient.

With respect to the hot weather adhesion of the polyester film and the UV curable resin, portable equipment has to withstand condensation in bathrooms, hot and humid areas, cold climates and the like, and it is necessary to maintain the adhesive force of the polyester film even under harsh conditions in the lamination process, So that adhesion is required. Up to now, the moisture resistance test has been carried out for 250 to 500 hours, but the trend is to evaluate the shortness of the test process water and the extreme conditions with a simple test. In this method, the adhesion is evaluated after 1 hour of treatment in boiling water .

Japanese Laid-Open Patent Publication No. 2013-41330 Korean Patent Publication No. 10-2007-0050570

The present invention has been accomplished in order to solve the above-mentioned problems and to solve the problems of the prior art. The object of the present invention is to provide a primer layer which is formed by applying a UV curable resin on a primer layer, And to provide an optical polyester laminated film capable of adjusting the refractive index and improving adhesion between the UV curable resin layer and the polyester film and hot water adhesion.

These and other objects and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof.

The above object is achieved by an optical polyester laminated film for optical use which comprises a base film and a coating layer on at least one side thereof, wherein the coating layer is formed from an aqueous coating liquid containing a polyurethane resin, a carbodiimide curing agent and a melamine curing agent Lt; / RTI >

Here, the coating liquid may be 60 to 91% by weight of a polyurethane resin, 8 to 35% by weight of a carbodiimide-based curing agent, and 1 to 25% by weight of a melamine-based curing agent.

Preferably, the refractive index of the coating layer is 1.53 to 1.61, the thickness is 50 to 150 nm, and the thickness of the base film may be 20 to 300 μm.

Preferably, the polyurethane resin may be composed of at least one of a polyurethane resin derived from a polyester polyol containing an aromatic carbonic acid component and a polyurethane resin containing acrylol.

Preferably, the carbodiimide-based curing agent may be one in which the chemical equivalent of the carbodiimide group is 300 to 600 and the terminal thereof is modified with polyethylene glycol.

Preferably, the melamine-based curing agent may be one in which 90% or more of the reactors are cured by a self-condensation reaction to improve the coating strength of the coating layer.

Preferably, the optical polyester laminated film is coated with a solvent or solventless type UV curable resin that imparts an optical function, then heat-treated in boiling water for 2 hours, and then the adhesive property with the UV curable resin layer may be 90% or more have.

According to the present invention, it is possible to prevent color unevenness after processing a UV curable resin, in particular a solventless UV curable resin, in an optical polyester laminated film, and to improve adhesiveness and hot water adhesion.

However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. It will be apparent to those skilled in the art that these embodiments are provided by way of illustration only for the purpose of more particularly illustrating the present invention and that the scope of the present invention is not limited by these embodiments .

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. Also, although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

In describing and / or claiming the present invention, the term "copolymer" is used to refer to a polymer formed by copolymerization of two or more monomers. Such copolymers include binary copolymers, terpolymers, or higher order copolymers.

The optical polyester laminated film according to an embodiment of the present invention comprises a substrate film having a coating layer on at least one side thereof, wherein the coating layer is formed of a coating liquid containing a polyurethane resin, a carbodiimide-based curing agent and a melamine-based curing agent .

The polyurethane resin contains a urethane bond or a urea bond which does not hydrolyze well and is favorable to hot water adhesion. A polyester polyol containing an aromatic carboxylic acid component, specifically, a naphthalene dicarboxylic acid and a derivative thereof or a phthalic acid derivative thereof is reacted with a glycol to prepare a polyester polyol so that the refractive index can be 1.55 to 1.61, A polyurethane resin is prepared by condensation reaction with a polyisocyanate or a polycarbodiimide in order to introduce urea bonds into a polyurethane resin which is easy to control the refractive index and then a coating layer having improved crosslinking density by using a carbodiimide crosslinking agent and a melamine crosslinking agent . The polyurethane resin is preferably used in an amount of 60 to 91% by weight based on the total weight of the coating liquid.

The average directional refractive index in the plane direction of the polyester film for optical use is about 1.65, and when the UV curable resin is applied, the resin layer has a value lower than that. For example, since the index of refraction of the acrylic hard coat layer is about 1.50, the refractive index difference between them is as large as about 0.15, resulting in irregularities in reflectance, that is, color unevenness. Particularly, in the case of a triple-wavelength fluorescent lamp that emits light in a specific narrow wavelength range, variations in ripple caused by variation in the thickness of the hard coat layer and overlapping of the light emitting wavelength region become large in the corresponding narrow light emission wavelength range, resulting in color unevenness. Therefore, it is possible to reduce the amplitude of the ripple by including a primer layer having a refractive index intermediate between that of the polyester film and the UV curable resin layer.

That is, when the refractive index of the primer layer is close to the refractive index of the UV curable resin layer, the refractive index difference with the optical polyester laminated film becomes large, so that the amplitude of the ripple increases and color irregularity occurs. When the primer layer has a large refractive index exceeding 1.61, The refractive index of the polyester laminated film becomes closer to that of the UV curable resin layer, so that the amplitude of the ripple increases and rainbow occurs. Therefore, it is advantageous to have a value intermediate between the refractive indexes of the UV curable resin layer and the optical polyester laminated film. In order to remarkably reduce the color unevenness in the visible light region (380 to 780 nm) 150 nm, and more preferably 70 to 120 nm. If it is thinner than 50 nm, the reflectance of the infrared region rises and the reddish color is visible. If it is thicker than 150 nm, the reflectance of the ultraviolet region is high and the purple color is visually recognized.

As a method for solving such color unevenness, it is necessary to set the refractive index to 1.55 to 1.61. This is because a polyurethane resin derived from a polyester polyol containing an aromatic carbonic acid component as a main chain and a polyurethane resin containing acrylol It can be solved by using a resin having a high refractive index including at least one or more.

In the present invention, it is also possible to contain an aromatic compound or an inorganic particle in order to increase the refractive index of the primer layer within a range that does not impair the effect of the present invention.

In one embodiment of the present invention, the carbodiimide-based curing agent is a compound having a carbodiimide structure and a compound having at least one carbodiimide structure in the molecule. A carbodiimide-based curing agent having a plurality of carbodiimide groups is more preferable.

In one embodiment of the present invention, the chemical equivalent of the carbodiimide group contained in the carbodiimide-based curing agent is preferably 300 to 600. To improve the water dispersibility and improve the stability of the coating liquid, For example, ethylene glycol or the like is preferably modified (bonded). The carbodiimide type curing agent is preferably 8 to 40% by weight of the total weight of the coating liquid. And more preferably 8 to 35% by weight. If it is less than 8% by weight, there is a disadvantage that the degree of curing of the coating layer is not sufficient, and when it exceeds 35% by weight, there is a disadvantage in that a sufficient adhesion with a UV curable resin can not be secured.

In one embodiment of the present invention, the melamine-based curing agent can be prepared by a conventional method, and at least 90% of the reactants through heat are self-polymerized by the self-condensation reaction to achieve a high film strength of the applied layer, The amount of 1 wt% of the total weight of the coating liquid greatly contributes to the hot water adhesion, but if it exceeds 25 wt%, the adhesion is deteriorated.

In one embodiment of the present invention, when the carbodiimide-based curing agent is used alone, the adhesion of the UV curing-type resin and the primer layer (coating layer) significantly deteriorates, and when the melamine-based curing agent is used alone The adhesion to the UV curable resin becomes very weak. Particularly, in the case of solvent-free UV curing type resin, it becomes more serious. Therefore, it is preferable to use a mixture of a carbodiimide-based curing agent and a melamine-based curing agent.

The adhesion between the UV curable resin layer and the primer layer (coating layer) is a basic property, but it is necessary that the adhesive force is maintained even after the resistance to water resistance is evaluated. In the present invention, the adhesion is preferably 90% or more, more preferably 95% or more, and even more preferably 100% after 2 hours of precipitation in boiling water. In order to realize such a high water bath adhesion, it is preferable to include a mixture of a carbodiimide-based curing agent and a melamine-based curing agent in the primer layer. A polyurethane resin exhibiting high adhesion with a UV curable resin and a carbodiimide curing agent having a high reactivity at a low temperature are sufficiently crosslinked in a curing process and a melamine curing agent causes a self-condensation reaction to make the primer layer more rigid The penetration of moisture is prevented to prevent a decrease in adhesion due to the hydrolysis of the urethane resin, so that the adhesiveness can be maintained even in a high-temperature and high-humidity environment.

In an embodiment of the present invention, various additives such as a surfactant, a solvent, an antioxidant, a heat stabilizer, a heat stabilizer, a heat stabilizer, a heat stabilizer, and a heat stabilizer may be added to a range not deteriorating the effects of the present invention, specifically, A weathering stabilizer, an ultraviolet absorber, an organic lubricant, a pigment, a dye, an organic or inorganic fine particle, a filler, an antistatic agent, a nucleating agent and the like. Particularly, the addition of the inorganic particles to the primer layer is more preferable because the running property and the blocking resistance are improved. In this case, as the inorganic particles to be added, silica, colloidal silica, alumina, alumina sol, kaolin, talc, mica, calcium carbonate and the like can be used.

However, in applications where transparency of the optical polyester laminated film is required, attention should be paid to the size and amount of added particles. The inorganic particles used in the optical application preferably have an average particle diameter of 0.005 to 3 mu m, more preferably 0.01 to 1 mu m, and most preferably 0.02 to 0.3 mu m. The mixing ratio of the inorganic particles to the resin in the primer layer is 0.05 - Is preferably 10% by weight, more preferably 0.1 to 5% by weight.

It is preferable that the primer layer of the present invention is provided by an in-line coating method described below using an aqueous coating liquid. Examples of the aqueous polyurethane resin composition include those obtained by dispersing the polyester polyol in an aqueous medium (water and, if necessary, containing an organic solvent) and an aqueous polyisocyanate dispersion. A surfactant may be added thereto. The aqueous polyisocyanate dispersion refers to, for example, a hydrophilic polyisocyanate having a nonionic hydrophilic group-containing compound introduced into a hydrophobic polyisocyanate obtained from an organic polyisocyanate containing two or more isocyanate groups in one molecule, And a self-emulsifiable polyisocyanate excellent in water dispersion stability which can be obtained by mixing an activator.

As a preferred method for forming the primer layer during the production of the optical polyester laminated film according to the present invention, a method of stretching together with a film to be formed in the process of producing a polyester film is very preferable, A method of providing by a coating method during a film forming process is most suitable. When considering the influence on the environment or the human body, it is preferable to use a water-based paint containing a water-dispersible solid matter containing water as a solvent rather than a paint mainly composed of a solvent.

The coating method on the film substrate can be carried out by various coating methods such as a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a Meyer bar coating method, a die coating method and a spray coating method. Further, the surface may be subjected to corona treatment or plasma treatment in consideration of uniformity of application of the coating film and adhesion.

In one embodiment of the present invention, the base film may be variously applied, but it is preferably a polyester base film. It is preferable that the base film has transparency capable of sufficiently transmitting visible light and has heat resistance, mechanical strength, and dimensional stability to withstand higher order processes. Most preferably a biaxially stretched PET film in terms of thermal and mechanical stability. If the thickness of the base film is 20 mu m or less, there is a shortage in thermal and mechanical stability. If the thickness is 300 mu m or more, the rigidity is too high and the handling property is deteriorated.

Since the optical polyester laminated film according to the present invention is used for optical use, the total light transmittance is preferably 90% or more, and the haze of the entire laminated film is preferably 2% or less, more preferably 1.5% And more preferably 1% or less. If the total light transmittance is less than 90%, when the laminated film is provided on the surface of the article, the brightness of the flat panel display may be reduced and the original color of the article may appear dark. Further, if the haze exceeds 2%, the laminated film may be peeled off when the laminated film is placed on the surface of the article, which may undesirably result in appearance of the article such as a flat panel display or household appliance.

The biaxially stretched polyester film is produced by melting and supplying a polyester obtainable by polymerizing a dicarboxylic acid type and a glycol type to a known extruder, And is preferably a film obtained by making the film into an unstretched sheet by cooling and solidifying the film by a method such as electrostatic application to the casting drum, followed by biaxial stretching and heat treatment.

Examples of the dicarboxylic acid used for the polyester resin include terephthalic acid, taftalene dicarboxylic acid, isophthalic acid, diphenylcarboxylic acid, diphenylsulfone dicarboxylic acid, phenoxyethanedicarboxylic acid, 5- Alicyclic dicarboxylic acids such as dicarboxylic acids, aromatic dicarboxylic acids such as dicarboxylic acid, dicarboxylic acid, dicarboxylic acid, dicarboxylic acid, dicarboxylic acid, dicarboxylic acid, Oxycarboxylic acids such as acetic acid, p-hydroxybenzoic acid, and the like can be used. Examples of the glycol used for the polyester resin of the film include aliphatic glycols such as ethylene glycol, propanol, butanediol, pentanediol, hexanediol, neopentin glycol and the like, and polyoxyethers such as diethylene glycol, polyethylene glycol and polypropylene glycol Alicyclic glycols such as alkylene glycol and cyclohexane dimethanol, aromatic glycols such as bisphenol A and bisphenol S, and the like. Considering the mechanical strength, weather resistance, chemical resistance, transparency, etc., it is preferable to use ethylene glycol as the former, and to the latter ethylene glycol as the latter. It is preferable to use an alkaline earth metal compound, a manganese compound, a cobalt chemical, an aluminum compound, an antimony compound, a titanium compound, a germanium compound or the like as a catalyst in the polymerization. The kind of dicarboxylic acid, the kind of glycol, or the catalyst may be used in combination of two or more kinds.

In addition, particles may be added to the film raw material in order to impart functions such as running property, weather resistance and heat resistance to the film, but sufficient attention must be paid to the addition amount and the material so as not to make the film transparent. The addition amount is preferably an extremely small amount, more preferably no addition. As for the running property (reverse activity) of the film, it is preferable to assist by adding particles of the laminated film as described above.

As the stretching method, known techniques such as biaxial stretching in the longitudinal direction and stretching in the transverse direction, and biaxial stretching in which stretching in the longitudinal direction and the transverse direction are simultaneously performed at the same time are used. The preheating temperature and the stretching temperature before stretching are 60 to 130 占 폚, and the stretching magnification is 2.0 to 5.0 times. If necessary, after stretching, heat treatment at 140 캜 to 240 캜 is carried out. Also, the amount of heat used at the time of stretching may be used to coat the laminated film with a water-based paint and then dry it.

Hereinafter, the structure and effect of the present invention will be described in more detail with reference to examples and comparative examples. However, this embodiment is intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

[Example 1]

Production Example 1: Preparation of coating liquid for preparing primer layer

13% by weight of a polyester polyol obtained by mixing naphthalene 2,6-dicarboxylic acid and 1,4-cyclohexane diol in a proportion of 30:70% by weight, 12% by weight of 4,4-diphenylmethane diisocyanate, Aqueous polyurethane resin (A) having a solids content of 25% by weight was prepared by adding 0.5% by weight of water and adding the remaining amount of water to prepare a water-based polyurethane resin (A).

Next, a carbodiimide curing agent (B), which is polymerized through the condensation reaction of a diisocyanate compound and has a chemical equivalent of 600 and a solid content of 40% by weight, is synthesized from hexamethylmelamine and 2-ethylhexane and partially alkoxymethylated, A melamine-based curing agent (C) having a content of 70% by weight was used.

The solid content of the coating liquid was adjusted to 5% by weight. To the mixture, 80% by weight of the aqueous polyurethane resin (A), 15% by weight of the carbodiimide curing agent (B) and 5% by weight of the melamine curing agent (C) Followed by mixing and dispersing to prepare a coating liquid for preparing a primer. The mixing ratio of the coating liquid is shown in Table 1 below.

Production Example 2: Production of optical polyester laminated film

Polyethylene terephthalate not containing a filler was melt-extruded at 280 DEG C and cast on a cooling drum of an electrostatically applied 20 DEG C to prepare a non-oriented sheet. The sheet was preheated to 100 DEG C, 3.0 times, and then the coating liquid for preparing the primer layer was applied on both sides of the film. Thereafter, it was preheated at 120 DEG C for 2 minutes, stretched 3.5 DEG in the transverse direction at 150 DEG C, and then heat-treated at 220 DEG C.

Through these processes, an optical polyester laminated film having a primer layer with a thickness of 100 nm formed on both sides was obtained. The thus obtained polyethylene terephthalate base film had an average refractive index in the plane direction of 1.665 and a refractive index of the primer layer of 1.59.

[Example 2]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was 80 wt% of the polyurethane resin (A), 18 wt% of the carbodiimide curing agent (B) and 2 wt% of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Example 3]

Except that the composition of the solid content in the coating liquid for preparing a primer layer was 70% by weight of the polyurethane resin (A), 28% by weight of the carbodiimide curing agent (B) and 2% by weight of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Example 4]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was 70 wt% of the polyurethane resin (A), 20 wt% of the carbodiimide curing agent (B) and 10 wt% of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Example 5]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was 60 wt% of the polyurethane resin (A), 20 wt% of the carbodiimide curing agent (B) and 20 wt% of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Example 6]

Except that the composition of the solid content in the coating liquid for preparing a primer layer was changed from 60 parts by weight of the polyurethane resin (A), 35 parts by weight of the carbodiimide curing agent (B) and 5 parts by weight of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 1]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was 70 wt% of the polyurethane resin (A), 30 wt% of the carbodiimide curing agent (B) and 0 wt% of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 2]

Except that the composition of the solid content in the coating liquid for preparing a primer layer was 70% by weight of the polyurethane resin (A), 0% by weight of the carbodiimide curing agent (B) and 30% by weight of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 3]

Except that 90% by weight of the polyurethane resin (A), 5% by weight of the carbodiimide curing agent (B) and 5% by weight of the melamine curing agent (C) were used in the coating liquid for preparing the primer layer. 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 4]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was 50% by weight of the polyurethane resin (A), 40% by weight of the carbodiimide curing agent (B) and 10% by weight of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 5]

Except that the composition of the solid content in the coating liquid for preparing a primer layer was such that 80 wt% of the polyurethane resin (A), 19.5 wt% of the carbodiimide curing agent (B) and 0.5 wt% of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 6]

Except that the composition of the solid content in the coating liquid for preparing the primer layer was changed from 60 parts by weight of the polyurethane resin (A) to 10 parts by weight of the carbodiimide curing agent (B) and 30 parts by weight of the melamine curing agent (C) 1 to obtain an optical polyester laminated film in which a primer layer was formed on both sides. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 7]

Except that the thickness of the primer layer was 40 nm. Thus, an optical polyester laminated film having a primer layer formed on both surfaces thereof was obtained. The mixing ratio of the coating liquid is shown in Table 1 below.

[Comparative Example 8]

Except that the thickness of the primer layer was 250 nm. Thus, an optical polyester laminated film having a primer layer formed on both surfaces thereof was obtained. The mixing ratio of the coating liquid is shown in Table 1 below.

Properties were measured by the following experimental examples using the polyester films for optical films according to Examples 1 to 6 and Comparative Examples 1 to 8, and the results are shown in Table 1 below.

[Experimental Example]

(1) Measurement of refractive index

The resin used for the primer layer was dried and solidified, and the refractive index was measured using a Abbe refractometer manufactured by Atago Co. for a film having a coating thickness of about 1 mm. The light source was a sodium lamp (Na-D line), and the mounting solution was a methylene chloride. The refractive index was measured by measuring the refractive index in two directions perpendicular to each other at 23 ° C and a relative humidity of 65%.

(2) Thickness of primer layer

The cross section of the laminated biaxially stretched polyester film was cut out in the freezing and ultraviolet cutting method, and the observation and photographs of the laminated film portion at an acceleration voltage of 100 kv were carried out using a transmission electron microscope H-7100 FA type manufactured by Hitachi, I shot it. From the cross-sectional photograph, arbitrary five laminated film thicknesses were calculated from the enlargement magnification and averaged.

(3) Measurement of color unevenness

The polyurethane was treated with hard coating (refractive index 1.50) and then the other side was treated with a black tape and evaluated in the dark room under the environment of a three-wavelength lamp according to the following criteria.

○: The color unevenness is not seen, and the uniform color is seen

?: The color uneven phenomenon appears soft depending on the angle and shows uniform color tone

X: The color stain is strong, and the stain color is strong.

(4) Average refractive index in the plane direction of the polyester laminate film for optical use

Using a Abbe refractometer manufactured by Atago Co., Ltd., the light source is a sodium lamp (Na-D line), the mount liquid is methylene chloride, and the birefringence index in the long direction and the width direction is measured at 23 ° C and a relative humidity of 65% The average value of the refractive index in the width direction was taken as the surface direction average refractive index. Since the primer layer is as thin as about 100 mm, in this measurement, the refractive index of the biaxially stretched polyester film was found.

(5) Evaluation of adhesion

UV-curable resin was applied to the surface to which the primer layer was adhered using a # 18 wire bar, a cut line was formed on the film coated with the primer layer by irradiating 300 mJ of UV with a cutter, and 2 mm × 2 mm squares were arranged. Cellulose tape (No. 405, made by NICHIBAN; width: 24 mm) was attached to the cut line film, and the tape was rubbed with velvet and strongly adhered to the film, and then the tape was vertically peeled off. The area of the primer layer remaining on the coating layer was visually observed, and the adhesive force was calculated by the following equation (1).

&Quot; (1) "

(6) Evaluation of hot water adhesion

Using a # 18 wire bar, a solvent-free UV-curable resin was applied to the surface to which the primer layer was adhered, irradiated with 300 mJ of UV, and the film was placed in boiling water (100 ° C) And cut lines were formed on a film coated with a primer layer by a cutter, and 2 mm x 2 mm squares were arranged in a 10 x 10 matrix. Cellulose tape (No. 405, made by NICHIBAN; width: 24 mm) was attached to the cut line film, and the tape was rubbed with velvet and strongly adhered to the film, and then the tape was vertically peeled off. The area of the primer layer remaining on the coating layer was visually observed, and the adhesive force was calculated by the above formula (1).

A
(wt%) B
(wt%) C
(wt%) Refractive index Primer layer
Thickness (nm) Rainbow Adhesiveness Hot water
Adhesiveness Example 1 80 15 5 1.59 100 ○ 100 100 Example 2 80 18 2 1.59 100 ○ 100 90 Example 3 70 28 2 1.58 100 ○ 100 90 Example 4 70 20 10 1.58 100 ○ 100 100 Example 5 60 20 20 1.57 100 △ 90 90 Example 6 60 35 5 1.57 100 △ 90 90 Comparative Example 1 70 30 0 1.57 100 ○ 90 50 Comparative Example 2 70 0 30 1.58 100 ○ 40 30 Comparative Example 3 90 5 5 1.60 100 △ 70 50 Comparative Example 4 50 40 10 1.56 100 X 70 50 Comparative Example 5 80 19.5 0.5 1.59 100 ○ 100 70 Comparative Example 6 60 10 30 1.57 100 △ 80 70 Comparative Example 7 80 15 5 1.59 40 X 100 100 Comparative Example 8 80 15 5 1.59 250 X 90 90

As can be seen from the above Table 1, the Examples are superior to the Comparative Examples in terms of color unevenness, adhesion between the primer layer and the UV curable resin layer as well as hot weather adhesion. In order to reduce color unevenness, it is necessary to control the refractive index and thickness of the primer layer in Examples and Comparative Examples 3, 4, 7, and 8. When the melamine-based curing agent is not used as in Comparative Example 1, the adhesion is excellent but it is very weak in the hot-water adhesion. When the carbodiimide-based curing agent is not used as in Comparative Example 2, it is difficult to obtain sufficient adhesion. From this, it can be seen that when the carbodiimide-based curing agent and the melamine-based curing agent are mixed, there is an effective effect on the adhesion and the hot water adhesion.

As can be seen from the above examples, when the polyurethane resin present in the primer layer is 60 to 91% by weight, the carbodiimide curing agent is 8 to 35% by weight and the melamine curing agent is 1 to 25% by weight, It can be confirmed that a primer layer having excellent adhesion is formed. It can be seen that when the primer layer is formed with other constitution, it shows poor adhesion as the result of the above comparative examples.

It is to be understood that the present invention is not limited to the above embodiments and various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (7)

A base film having a coating layer on at least one side thereof,
Wherein the coating layer is formed from an aqueous coating liquid containing a polyurethane resin, a carbodiimide-based curing agent, and a melamine-based curing agent. The method according to claim 1,
Wherein the coating liquid contains 60 to 91% by weight of a polyurethane resin, 8 to 35% by weight of a carbodiimide-based curing agent and 1 to 25% by weight of a melamine-based curing agent. The method according to claim 1,
Wherein the coating layer has a refractive index of 1.53 to 1.61, a thickness of 50 to 150 nm, and a thickness of the base film of 20 to 300 占 퐉. 3. The method of claim 2,
Wherein the polyurethane resin comprises at least one of a polyurethane resin derived from a polyester polyol containing an aromatic carbonic acid component and a polyurethane resin containing acrylol. The method according to claim 1,
Wherein the carbodiimide-based curing agent is characterized in that the chemical equivalent of the carbodiimide group is from 300 to 600 and the terminal is modified with polyethylene glycol. The method according to claim 1,
Wherein the melamine-based curing agent is characterized in that at least 90% of the reactors cause a curing reaction by a self-condensation reaction to improve the coating strength of the coating layer. 7. The method according to any one of claims 1 to 6,
Wherein the optical polyester laminated film is coated with a solvent or solventless type UV curable resin for imparting an optical function and then heat-treated in boiling water for 2 hours, and then the adhesive property to the UV curable resin layer is 90% or more. Polyester laminated film for optical use.